The embodiments described herein relate generally to a system that employs x-ray diffraction imaging (XDI) and, more particularly, to an XDI system that identifies objects through aggregation of signals in multiple contiguous voxels.
Known security detection systems are used at travel checkpoints to inspect carry-on and/or checked bags for concealed weapons, narcotics, and/or explosives. At least some known security detection systems include x-ray imaging systems. In an x-ray imaging system, an x-ray source transmits x-rays through an object or a container, such as a suitcase, towards a detector, and the detector output is processed to identify one or more objects and/or one or more materials in the container.
At least some known XDI systems provide an improved discrimination of materials, as compared to that provided by other known x-ray imaging systems, by measuring d-spacings between lattice planes of micro-crystals in materials. Further, x-ray diffraction may yield data from a molecular interference function that may be used to identify other materials, such as liquids, in a container.
Known multi-detector inverse fan beam (MIFB) XDI systems feature an x-ray multisource emitting a multiplicity of polychromatic x-ray beams, such that each object voxel is irradiated from several different directions. These systems measure spatially-resolved x-ray diffraction profiles of the constituent voxels of inhomogeneous, extended objects. Such MIFB XDI systems generate a three-dimensional (3D) volumetric map, or image, where each voxel within the image includes the polychromatic energy spectrum, i.e., the momentum transfer profile for coherent scatter signals originating from each voxel. Some of these known MIFB XDI systems use relatively small voxels to improve visual resolution of smaller object features. However, as defined by the number of photons measured per voxel, the signal level from each voxel is very low. In general, performance of XDI systems decreases significantly when there are less than 100 photons per voxel. In some known XDI systems, the photon count is in the range between 0 and 25 photons per voxel.
Therefore, due to these low signal levels, it is difficult to establish reliable spectra for accurate material characterization in individual voxels. Objects of interest typically occupy multiple contiguous voxels and such objects of interest may be positioned proximate and/or adjacent to each other. A simple aggregation of signals from adjacent, or nearby voxels may provide sufficient material spectra to accurately identify a substance of interest. However, if the selection of combined voxels includes voxels with photons scattered from different materials, then the resulting spectrum will be a mixture and it may not be possible to identify the materials. In addition, visual discrimination of proximate and/or adjacent objects of interest may be difficult to generate.